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Rana and Sharma (2017) dispute our tectonic interpretation mainly on the basis of what they believe (climate?). However, we welcome their comments, as this gives us a chance to highlight the ambiguity inherent in discriminating the climate-tectonic imprints in morphotectonic records that are prevalent in current research. We should note that the paper published by Kothyari et al. (2017) was reviewed by national/international reviewers. We would like to emphasize the fact that the paper does not rule out the role of climate. However, most importantly, it presents significant features and observations that collection/assemblage points toward the dominant role of tectonics in their shaping, and not solely climate, as postulated by Rana and Sharma (2017). The objective of this paper is to identify tectonic signatures (geomorphology) in a monsoon - dominated, tectonically active terrain like the North Almora Thrust (NAT). These faults are marked by previous workers based on field evidence such as folding and faulting of lithological units; presence of slickensides parallel to the fault; offset of NAT owing to a transverse fault; and offset of drainage, drainage basin analysis, strath terraces, fluviolacustrine terraces, development of scarp, narrow river course, and deeply incised valleys. However, we disagree with the comments raised by Rana and Sharma (2017), because they are highly skewed toward the climate school of thought, and did not perceive the setting as a collection of landforms. Instead, they attempted to view them in isolation. Because these comments are important, we will try to further our research incorporating issues related to isolation of climate and tectonics imprints in the immediate future. We would like to thank Rana and Sharma (2017) for raising some basic questions on our work as this gave us an excellent opportunity to summarize and present the dominance of various processes and related landforms as earlier reported by Kothyari et al. (2017). A point-by-point detailed rebuttal/explanation of their queries is provided below. [ABSTRACT FROM AUTHOR]

The landform development and valley floor morphology of active regions is significantly controlled by tectonic processes. In the present study the upper catchments of Kosi and Gagas river valleys have been investigated with special emphasis on aggradational landforms to explain the spatial and temporal variability of aggradation/incision in response to tectonic activity during the late Quaternary and Holocene in Central Kumaun Himalaya. Major tectonic elements such as the North Almora thrust (NAT), Rasiyari fault (RF), and Gagas fault (GF) are considered to be controlling the development of landforms in the region. The valleys have preserved debris flow terraces, bedrock strath terraces, and fluviolacustrine terraces that provide signatures of tectonic activity. Morphostratigraphy of the terraces reveals that the oldest landforms are preserved in the hanging wall block of the NAT, RF, and along the GF. Reconstructions based on morphostratigraphy through the application of optical chronology suggests multiple phases of fluvial aggradation in the upper catchment of the Kosi and Gagas rivers that were initiated around 34 ka. The youngest phase of aggradation is dated to be around early to mid-Holocene (7–1 ka). Based on terrace morphology, four major phases of enhanced uplift have been estimated during 34, 15.8, 7, and 3 ka. The older uplift event dated to be around 34 ka is represented uplift along GF, which accommodated onset of valley-fill aggradation in Gagas valley. The 15.8 ka event represents uplift along RF, which led to the generation of debris flow from adjacent hillslopes. The 7 ka event represents uplift of a hanging wall block of the NAT and deposition of debris flow terraces. However, the youngest 3 ka event represents enhanced uplift, which is responsible for the incision of the older valley fill sediments and bedrock. Following this, a phase of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces between 7 and 1 ka. [ABSTRACT FROM AUTHOR]

The present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation/incision in response to tectonic activity during the late Quaternary in the Saryu River valley in central Kumaun Himalaya. The valley has preserved cut-and-fill terraces with thick alluvial cover, debris flow terraces, and bedrock strath terraces that provide signatures of tectonic activity and climate. Morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the Main Central Thrust, the fluvial modified debris flow terraces, were developed between 30 and 45 ka. The major phase of valley fill is dated between 14 and 22 ka. The youngest phase of aggradation is dated at early and mid-Holocene (9–3 ka). Following this, several phases of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces. Seven major phases of bedrock incision/uplift have been estimated during 44 ka (3.34 mm/year), 35 ka (1.84 mm/year), 15 ka (0.91 mm/year), 14 ka (0.83 mm/year), 9 ka (1.75 mm/year), 7 ka (5.38 mm/year), and around 3 ka (4.4 mm/year) from the strath terraces near major thrusts. We postulate that between 9 and 3 ka the terrain witnessed relatively enhanced surface uplift (2–5 mm/year). [ABSTRACT FROM AUTHOR]

In present study the results of integrated studies of landform development and geomorphic indices of drainage networks across the South Wagad Fault (SWF) zone have been presented. The SWF is a structure that is morphogenic in nature, creating a 40-m-high E–W trending escarpment that extends ~ 80 km at the southern end of the Wagad uplift. The SWF got reactivated during the Bhuj earthquake of 2001, continued aftershock activity of M ≥ 4 levels were recorded in the epicentral zone, north of the Kachchh Mainland Fault and west of the SWF. Strath terraces along the river valleys and the truncation of alluvial fans along the mountain front, incision, and offset of rivers suggests an active nature of the SWF. To assess the relative tectonic activity, morphometric indices such as stream-gradient ( SL ) index, hypsometric integral ( HI ), basin asymmetry ( AF ), mountain front sinuosity ( S mf ) index, sinuosity index ( SI ), and basin shape ( B S ) have been analyzed. The landform development along the river valley in the SWF zone suggests reactivation of the SWF between 12 and 3 ka. The southern front of Wagad is found to be uplifting at the rate of 2.8 mm/y during the last 12 ka as estimated through OSL dates. The relative index of active tectonics (RIAT) by the study of different geomorphic parameters and field checks indicates that most of the Wagad highland is active. The compressional strain of 0.05 μstrain/y inferred from the GPS study in the SWF area attests to the activeness. [ABSTRACT FROM AUTHOR]

Structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern Arunachal sub-Himalaya. Mountain front sinuosity ( S mf ) index values close to one are indicative of the active nature of the mountain front all along the eastern Arunachal Himalaya, which can be directly attributed to the regional uplift along the Himalayan Frontal Thrust (HFT). However, the mountain front is significantly sinusoidal around junctions between HFT/MBT (Main Boundary Thrust) and active transverse faults. The high values of stream length gradient ( SL ) and stream steepness ( K s ) indices together with field evidence of fault scarps, offset of terraces, and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults. This reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses, providing favourable sites for deposition of recent sediments. Tectonic interactions of these transverse faults with the Himalayan longitudinal thrusts (MBT/HFT) have segmented the mountain front marked with varying sinuosity. The net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements. Some distinctive examples are: in the eastern extremity of NE Himalaya across the Dibang River valley, the NW-SE trending mountain front is attenuated by the active Mishmi Thrust that has thrust the Mishmi crystalline complex directly over the alluvium of the Brahmaputra plains. The junction of the folded HFT and Mishmi Thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the Dibang River course. Similarly, the transverse faults cut the mountain front along the Sesseri, Siluk, Siku, Siang, Mingo, Sileng, Dikari, and Simen rivers. At some such junctions, landforms associated with the active right-lateral strike-slip faults are superposed over the earlier landforms formed by transverse normal faults. In addition to linear transverse features, we see evidence that the fold-thrust belt of the frontal part of the Arunachal Himalaya has also been affected by the neotectonically active NW-SE trending major fold known as the Siang antiform that again is aligned transverse to the mountain front. The folding of the HFT and MBT along this antiform has reshaped the landscape developed between its two western and eastern limbs running N-S and NW-SE, respectively. The transverse faults are parallel to the already reported deep-seated transverse seismogenic strike-slip fault. Therefore, a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the Himalayan region must take into account the role of transverse tectonics. [ABSTRACT FROM AUTHOR]

We present the results of integrated studies of geomorphic indices of drainage networks and landforms developed across the mountain front along the Himalayan Frontal Thrust (HFT) between the Dabka and Baur rivers, Kumaun Himalaya. The HFT is a morphogenic structure in nature, creating a 100-m-high E–W trending escarpment that extends ~ 21 km. Geomorphological evidence indicates ~ 10.5 km westward migration of the Dabka River and ~ 5.2 km eastward migration of the Baur River. These migrations are a result of uplift of the hanging wall along the HFT. The HFT is offset by a transverse fault, which suggests that the latter postdates the reactivation of the HFT between 500 and 100 ka. Presence of different levels of strath terraces along the mountain front suggests the active nature of the HFT. To assess the relative tectonic activity, morphometric indices such as stream-gradient ( SL ) index, mountain front sinuosity ( S mf ) index, and ratio of valley floor width to valley height ( Vf ) have been analyzed. Results of the former two are consistent with the tectonic landforms developed in thrust zones. Paleochannels of the Dabka and Baur rivers are characterized by high Vf values while other valleys show low Vf values. Quaternary alluvial sediments have been deformed along the Pawalgarth Thrust, a splay of the HFT. Deformation has resulted in the formation of the Pawalgarh Anticline, a thrust-related asymmetric fold. [ABSTRACT FROM AUTHOR]